Sulfonated block copolymers (SBCs) are known in the art and described, e.g., in U.S. Pat. No. 3,577,357; U.S. Pat. No. 3,642,953; U.S. Pat. No. 3,870,841; U.S. Pat. No. 4,492,785; U.S. Pat. No. 4,505,827; U.S. Pat. No. 5,239,010; U.S. Pat. No. 5,468,574; U.S. Pat. No. 5,516,831; U.S. Pat. No. 6,110,616; U.S. Pat. No. 7,169,850; U.S. Pat. No. 7,737,224; WO 2008/089332, and WO 2009/137678. They are typically prepared by sulfonating a corresponding non-sulfonated block copolymer in one or more organic solvents using sulfonating agents such as, e.g., sulfur trioxide or acyl sulfates. Since the SBCs are valuable materials, e.g., for the manufacture of membranes and films, coagulation of the SBC from the organic solution frequently is accomplished by directly casting the SBC solution obtained in the sulfonation reaction. E.g., U.S. Pat. Nos. 3,642,953; 5,468,574; U.S. Pat. No. 6,110,616; U.S. Pat. No. 7,169,850; U.S. Pat. No. 7,737,224; WO 2008/089332, and WO 2009/137678. However, the coagulation of the SBC solution via film casting is disadvantageous in various regards. For example, the method is not well suited to post coagulation washing to remove impurities. Additionally, storage of the films or membranes is disadvantageous because the films or membranes are low in bulk density hence requiring more packaging and storage space. Also, when the membrane or film is to be stored in rolled-up form, it is necessary to insert a liner between the rolled layers to prevent sticking which further increases expenditures.
In addition to coagulating the SBCs by way of membrane casting, it has been mentioned that the SBCs can be coagulated by steam stripping the SBC solution and subsequently washing the SBC residue thus obtained with boiling water. E.g., U.S. Pat. No. 5,239,010; U.S. Pat. No. 5,516,831; U.S. Pat. No. 7,169,850; and U.S. Pat. No. 7,737,224. It has been observed, however, that steam stripping causes severe foaming, especially when the SBC is sulfonated to a high degree, which can render this approach unsuited for large scale and economic coagulation of the SBCs.
The coagulation of a non-sulfonated block copolymer from its solution generally can be achieved by one of three methods. Firstly, the solvent(s) can be evaporated by heating the block copolymer to its melting temperature. Secondly, the solution can be combined with steam and the solvent(s) can be evaporated in a cyclone or similar device. Thirdly, the solution can be pre-mixed with steam and the mixture can be ejected into or onto preheated water to evaporate the solvent(s). However, the coagulation methods conventionally used for coagulating a non-sulfonated block copolymer have been found to be inadequate for the coagulation of SBCs from a solution in one or more organic solvents.
The first method has been found to be unsuited for coagulating SBC solutions because SBCs are susceptible to degradation at elevated temperatures, especially when the copolymer solution which is employed is the reaction mixture obtained in the sulfonation of the block copolymer. Additionally, SBCs are more ‘sticky’ than their non-sulfonated counterparts. Accordingly, when the solvent(s) of the SBC solution are evaporated in a cyclone or similar device, the stickiness of the SBC causes excessive equipment fouling which renders the second method unsuited for coagulating SBC solutions. While premixing the solution with steam as well as ejecting the mixture in form of an atomized stream in accordance with the third procedure facilitates the formation of polymer particles of non-sulfonated block copolymers, the ‘stickiness’ of the SBCs causes fouling of the ejection nozzles under these conditions. In addition, similar to the problems encountered during steam stripping, excessive foaming occurs when a mixture of steam and the SBC solution is ejected into or onto the preheated water. It has further been observed that the mixture of the SBC, the solvent(s) and the water tends to form a dispersion of the SBC in the form of very small particles which cannot be readily separated by filtration or centrifuging. Coagulation agents which are customarily used in the coagulation of the non-sulfonated counterparts such as, e.g., polyvinyl alcohol and 2-ethylhexanol, have been found to be ineffective to overcome these problems encountered with the SBCs.
Accordingly, there continues to be a need for a process which allows the coagulation of SBCs. Such a process, preferably, should be easy to implement and should avoid or at least diminish the above mentioned problems. The process, also, preferably should be applicable for coagulating a solution of the SBC corresponding to the reaction mixture in which the SBC is generated. It would also be desirable that the process yield the SBC in a form such as particles which are easy to handle and which facilitate storage and further processing of the SBC.